Arecibo Observatory
The
Arecibo Observatory is located approximately 12 miles south-southwest from
Arecibo,
Puerto Rico (near the extreme southwestern corner of Arecibo
pueblo). It is operated by
Cornell University under cooperative agreement with the
National Science Foundation. The
observatory works as the
National Astronomy and Ionosphere Center (
NAIC) although both names are officially used to refer to it. NAIC more properly refers to the organisation that runs both the observatory and associated labs and offices at Cornell University.
The observatory's 305-m
radio telescope is the largest single-aperture telescope ever to be constructed. (Compare "
multiple aperture telescope".) It carries out three major areas of research:
radio astronomy,
aeronomy (using both the 305-m telescope and the observatory's
lidar facility), and
radar observations of
solar system objects. Usage of the telescope is gained by submitting proposals to an independent board of referees.
The telescope is visually distinctive and has been used in the filming of two notable motion pictures: as the villain's antenna in the
James Bond movie GoldenEye and as itself in the film
Contact. The telescope received additional international recognition in 1999 when it began to collect data for the
SETI@home project.
The Arecibo telescope is distinguished by its enormous size: the main collecting dish is 305 m in diameter, constructed inside the depression left by a
karst sinkhole. The dish is the largest curved focusing dish on Earth, giving Arecibo the largest electromagnetic-wave gathering capacity. The Arecibo telescope's dish surface is made of 38,778 perforated
aluminium panels, each measuring about 1 m by 2 m (3 ft by 6 ft), supported by a mesh of steel cables.
It is a
spherical reflector (as opposed to a
parabolic reflector). This form is due to the method used to aim the telescope: the telescope's dish is fixed in place, but the receiver at its focal point is repositioned to intercept signals reflected from different directions by the spherical dish surface. The receiver is located on a 900-ton platform which is suspended 150 m (450 ft) in the air above the dish by 18 cables running from three
reinforced concrete towers, one of which is 110 m (365 ft) high and the other two of which are 80 m (265 ft) high (the tops of the three towers are at the same elevation). The platform has a 93 m long rotating bow-shaped track called the
azimuth arm on which receiving antennae, secondary and tertiary reflectors are mounted. This allows the telescope to observe any region of the sky within a forty degree cone of visibility about the local
zenith (between -1 and 38 degrees of
declination). Puerto Rico's location near the
equator allows Arecibo to view all of the planets in the solar system except Pluto, which has been too far south since about 1989.
The construction of the Arecibo telescope was initiated by Professor
William E. Gordon of Cornell University, who originally intended to use it for the study of Earth's
ionosphere. Originally, a fixed parabolic reflector was envisioned, pointing in a fixed direction with a 150 m (500 ft) tower to hold equipment at the focus. This design would have had a very limited use for other potential areas of research, such as
planetary science and
radio astronomy, which require the ability to point at different positions in the sky and to track those positions for an extended period as Earth rotates.
Ward Low of the
Advanced Research Projects Agency (
ARPA) pointed out this flaw, and put Gordon in touch with the
Air Force Cambridge Research Laboratory (AFCRL) in Boston, Massachusetts where a group headed by
Phil Blacksmith was working on spherical reflectors and another group was studying the propagation of
radio waves in and through the upper atmosphere. Cornell University proposed the project to ARPA in the summer of 1958 and a contract was signed between the AFCRL and the University in November of 1959. Construction began in the summer of 1960, with the official opening taking place on
November 1,
1963. As the primary dish is spherical, its focus is along a line rather than at a single point (as would be the case for a parabolic reflector), thus complicated 'line feeds' had to be used to carry out observations. As the configuration of the line feeds is dependent on frequency and only two could be fitted at any one time, this limited the flexibility of the telescope.
The telescope has undergone several significant upgrades over its lifespan. The first major upgrade was in 1974 when a high precision surface was added for the current reflector. In 1997 a gregorian reflector system, incorporating secondary and tertiary reflectors to focus the radio waves at a single point. This allowed the installation of a suite of receivers, covering the whole 1-10 GHz range, that could be easily moved onto the focal point, giving Arecibo a flexibility it had not previously posessed. At the same time a ground screen was installed around the perimeter to prevent receivers from sensing the ground (which, due to its temperature, would make observations less sensitive) and a more powerful transmitter was installed.
The Arecibo telescope has made many significant scientific discoveries. On
7 April 1964, shortly after its inauguration,
Gordon H. Pettengill's team used it to determine that the
rotation rate of
Mercury was not 88 days, as previously thought, but only 59 days. In 1974
Hulse and
Taylor discovered the first binary pulsar
PSR B1913+16, for which they were later awarded the
Nobel Prize in Physics.
In August 1989, the observatory directly imaged an
asteroid for the first time in history:
asteroid 4769 Castalia. The following year, Polish astronomer
Aleksander Wolszczan made the discovery of
pulsar PSR B1257+12, which later led him to discover its three orbiting planets (and a possible comet). These were the first
extra-solar planets ever discovered.
The telescope also had
military intelligence uses, for example locating
Soviet radar installations by detecting their signals
bouncing back off of the
Moon. Arecibo is also the source of data for the
SETI@home distributed computing project put forward by the Space Sciences Laboratory at the
University of California at Berkeley and was used for the
SETI Institute's
Project Phoenix observations.
In 1974, the
Arecibo message, an attempt to communicate with extraterrestrial life, was transmitted from the radio telescope toward the
globular cluster M13, about 25,000 light-years away. The 1,679
bit pattern of 1s and 0s defined a 23 by 73 pixel
bitmap image that included numbers, stick figures, chemical formulas, and a crude image of the telescope itself.
From
March 3 to
March 7,
2001 the observatory was used to observe
asteroid (29075) 1950 DA, considered to be the most
Near-Earth object.
Terrestrial aeronomy experiments include the controversial (Ruiz 1998)
Coqui 2 experiment (Friedlander 1997).
Arecibo Observatory was used as a filming location in the final scene of the
James Bond movie
GoldenEye. In the film, the villain Alec Trevelyan used a similar dish in Cuba to communicate with a Russian satellite to fire an
electromagnetic pulse at London. This dish could be filled with water to conceal itself as a lake, a feat impossible at Arecibo due to its perforated surface. Additionally, the use of Arecibo to communicate with an earth-orbiting satellite is nonsensical from a technical standpoint.
The observatory was also featured in a segment of a
Reading Rainbow episode.
In the
X-Files episode "
Little Green Men",
Fox Mulder was sent to the Arecibo Observatory by a
U.S. Senator because contact had been made with extraterrestrial life. As was often the case in the series, Mulder was forced to escape as U.S. government military forces arrived, without taking definitive proof of alien contact with him.
The film
Contact features Arecibo in a more life-like way, as main character Ellie Arroway uses the facility as part of a
SETI project.
The Arecibo Observatory was also featured in the film
Species, as the main setting for
James E. Gunn novel
The Listeners (1972), and as a prominent element in the
Mary Doria Russell novel
The Sparrow (1996).
*
List of radio telescopes*
Sixto Gonzalez, Director of Arecibo Observatory
